Airplane approach control system



Sept. l2, 1950 o. s. FIELD x-:TAL 2,522,029

AIRPLANE APPROACH CONTROL SYSTEM nf@ m l l /k l 1 1 1 TT Y "1 1 "@on 3g, ql EN mnentors O eld, NWjght and RWHewes Bg WMM,

Their Gttorneg Sept. l2, 1950 o. s. FIELD ETAL AIRPLANE APPROACH CONTROL SYSTEM 1l Sheets-Sheet 2 Filed Jan. 22. 1945 /fa/d/fan Srmentors,

0.5. Field, NWI'g h and RW. Hawes E MMM Their Gttorneg Sept. 12, 1950 o. s. FIELD Erm.

AIRPLANE APPROACH CONTROL SYSTEM Filed Jan. 22. 1945 11 Sheets-Sheet 3 FIG. 5

:inventors O.5.Fe\d, NWigh and RWHewes W Their Gttorrxeg Sept. 12, 1950 o. s. FIELD ETAL 2,522,029

AIRPLANE APPROACH CONTROL SYSTEM Filed Jan. 22. 1945 l1 Sheets-Sheet 4 FIG. 6A 1441 U/'f C 3 :mentors Their Ctforneg Sept 12, 1950 o. s. FlELD ET AL 2,522,029

A RPLNEl APPROACH CNTROL SYSTEM Filed Jan. 22.A 1945 ll Sheets-Sheet 5 mentors Their Qttorneg GS Field, swwfqht Mdm/.Hawes Sept 12, 1950 o. s. FIELD ETAL 2,522,029

IRPLNE APPRACH CONTROL SYSTEM Filed Jan. 22. 1945 1l Sheets-Sheet 6 Oleld, NWqh and RWHewes Their (Ittorneg Sept 12, 195o o. s. FIELD UAL 2,522,029

AIRPLANE APPROACH CONTROL SYSTEM Filed Jan. 22. 1945 ll Sheets-Sheet 7 FIG. 7

Alt. J r A'L 07:/

40 cg 40 5506? 35 000@ if 00650@ 30 a/T/S/O`Q\ an 30 UCE/Q; Q9 07/ 2:00 00 25/00 06@ 200000 20 00 0@ 20 000g@ Snventors 0.5.Ff`eld- 5. NpWigh and 12M/.Hawes Their Cttorneg Sept. l2, 1950 o. s. FIELD ETAL AIRPLANE APPROACH CONTROL SYSTEM 1l Sheets-Sheet 8 Filed Jan. 22, 1945 .Qdi

Snoentors 0.5, Field, NWgh and RW Hewes .Duim

Their Cttox'neg Sept. 12, 1950 O o. s. FIELD ETAL AIRPLANE APPROACH CONTROL SYSTEM ll Sheets-Sheet 9 Filed Jan. 22. 1945 Bnnentors 05mm, smwfgm and RwHewe Their' Gtforneg Sept. l2, 1950 o. s. FIELD ETAM.v

AIRPLANE APPROACH CONTROL SYSTEM Filed Jan. 22. 1945 OField, SNVYiq and RWHewes Their attorney @L /@Tet Sept. 12, 1950 o. s. FIELD ET AL AIRPLANE APPROACH CONTROL SYSTEM 1l Sheets-Sheet 1l Filed Jan. 22. 1945 Qdi :Snventors Field, NWI'gh and QWHewcs Their (Ittor'neg Patented Sept. 12, 1950 UNITED STATES PATENT OFFICE' 2,522,029 AIRPLANE APPROACH CONTROL-SYSTEM oscar s. Field, Sedgwick Ni. Wighwmanalpnw, Howes, Rochester,- N. Y. assignors to Generall Railway Signal CmpanyRochester, NJY. ApplicationJanuary 22, 1945, Serial No. 573,876

35 Claims.

This invention relates to a control system in which computers or flight `predictors are used to compute approximately the time an airplane mustconsume in flying out into a variable length storage `loop in order to get into position to land at a predetermined time; and this invention may be considered an improvement. over the method and apparatus disclosed inthe prior application of S. P. Saint, Ser. No. 569,335, iiled December 22, 1944, now Pat. No. 2,495,139, dated January y17, 1950.`

It has been the common practice toV store airplanes in one or more storage stacks near an airport, each airplane being assigned toy fly 1n its particular altitude, and to then cause` these airplanesv to be landed one at a` time either d irectly-.from its altitude or after it had been laddered down toone of the lowest altitudes. By reason of the fact that theofperator or dispatcher who supervises such landing of Vairplanes from a storage stack does not know, at least under. poor visibility, in what part ofy thev flight pathr ini, his altitude a particular airplane is flyingwhen. its pilot is called to make a landing, it is necessary for this dispatcher to allow suflicient time be,- tween the successive calling of. airplanes.V from the holding stack to guard against any possible collision between two airplanes, and it isthis unnecessarily long time spacing between air.- planes `that is. to be avoided. fby the. use ofthe computer and associated apparatus involving the present invention.v

In accordance with the present invention; itis therefore proposed to provide a computer which is preferably automatically operated in accordance `with the lapse of time as determinedv by suitable time manifesting means such asian-elec,- tric motorof either the direct current or alter hating current synchronous type vto determine the time tobe consumed in flying out to the turn point in the holding loop.

Since the present inventionf contemplatesthe landingr oiairplanes in overlappedl relationship. by calling themfrom they holdingstack in shorter time spaced intervals than the time. period al-` lotted to a landing maneuver, itV isi proposed: to,

interconnected i that itv guards against. the; calling.l

of airplanes at shorter spaced time itnervals than a predetermined time interval` for,y which.

thecomputer has ibeen .designated or adjusted;y

ln accordance with another. objection the pres ent invention `it is iproposedto direct: aniairplane'.-

eithertothe right or. to the. lettofra particular;

to have this angle automatically indicated vby the computer at the instant the dispatcher must inform the pilot as to his procedure in the holding loop.

Also, since both head winds and tail Winds will have a Ibearing on the distance that an airplane is to ily` into the holding loop it is proposed, in accordance with another object of the present invention,I to have the proposed computer indicate such distance in part dependent upon whether there is a prevailing head wind or tail wind and in part in'. accordance with the time consumed-,in` the holding stack, these two wind compensating provisions lacing so constructed that if both a right or left component anda head or tail component are existent simultaneously this computer will indicate both the proper angle at. which the pilot is to fly into the holding loop and, also4 they distance he is to travel, expressed in time, lbefore he makes a procedural turn.

Another object of the present invention residesin automatically sounding a so-called peep-` peep signal a predetermined time before the pilot is to make a procedural turn so that he will not be entirely caught by surprise.

Another object of the present invention resides in the; provision of av number of indicating lamps for indicating when an airplane is in the course of 'being laddered down from. one altitude to another ina holding stack or holding loop and to providesuitafble indicating lamps for informing theloperator howlv the computer and manual-push button operation. iswprogressing during its computing operation.

Another object oftthe present invention resides in theprovision ofv tokens, token jacks and indieating` lamps for bothla dispatcher and a monitor, together with pushbuttons for the dispatcher, for governing and indicating the progress of the laddering down of airplanes in the holding stack.

Another feature of.y the' present invention re sides in the provision of timing means for properly.A time spacing the availability ofthe three unitsi of the computer;

More specically ity is proposed to provide a computer which'aannouncesgas bythe lighting of` aglamp,v that:anairplanevshalllbe called from the` holding stack, in the provision that another lamp that manifests that the. airplane-ibas actually 'entered the holding loop,;the. provision of still ann other: `lamp which manifests. that the airplane is to make a procedural turn and includes the provision of suitable push buttons operated by the operator at the proper times and which if operated determine the ultimate information predicted by the computer.

features of the system organization are claimed herein; whereas, the novel computerv structure and the interrelationship between the various parts of the computer structure are disclosed and claimed in the divisionalapplication Ser.'A No. 93,146, iiled May 13, 1949, and no claim'is intended to be made herein to such subject matter.

Other objects, purposes and characteristic features of the present invention will in part be understood from the accompanying specication and will in part be obvious from the accompanying drawings, in which:

Fig. 1 illustrates a portion of the flying lfield including a runway and two radio beacons or aerophares showing the flyingpattern for the holding stack and the flying pattern of holding loops of various sizes;

Fig. 2 illustrates a side view of the patterns illustrated in Fig. 1 illustrating airplanes at various altitudes;

Fig. 3 illustrates a simplified form of computer which may be used under rio-wind or substantially no-wind flying conditions;

Fig. 4 illustrates a timer used for timing the starting of successive units of the computer i1- lustrated in Figs. 8A and 8B;

Fig. 5 illustrates timer controlled stick relays controlled in part by the timer illustratedin Fig. 4 and in part by contacts operated by the three units of the computer illustrated 'in Figs. 8A and 8B;

Figs. 6A, 6B and 6C illustrate the circuits and relaysI used for controlling the computer illustrated in Figs. 8A and 8B;

Fig. '7 illustrates three control boards',l one for each of three operators each having three small panels one for each unit of the computer, and also illustrates the face of the computer illustrated in Figs. 8A and 8B;

Figs. 8A and 8B illustrate the preferred form of a three-unit computer used in connection with the circuits illustrated in Figs. 4, 5, 6A, 6B, 6C, 9 and 10 of the drawings;

Figs. 9 and 10 illustrate the laddering-down circuits controlled by the tokens illustratedv in Fig. '7 and by similar tokens located on a monitors board also conventionally illustrated in Fig. 9 by a dotted rectangle;

Fig. 1l illustrates in detail the multiplying plate I'I5 constituting part of Fig. 8B of theA drawings;

Figs. 12, '13, 14 and 15 illustrate flying patterns under a right wind, a left wind, a head wind and a tail wind, respectively;

Fig. 13A displays algebraic expressions used in the design of the multiplying plate illustrated in Fig. 1l of the drawings;

Fig. 16 shows the heading angle dials and time dials of Fig. '7 assuming indications in conformity with the normal condition reflected by the circuits illustrated in Figs. 4, 5, 6A, 6B and 6C, namely, with unit A assuming the minimum outtime position;

Fig. 17 shows the relationship between certain sheets of the drawings; and y i Fig. 18 illustrates a Lmodiiied flying pattern in connection with which the present invention may be practiced.

Holding stack and holding Zoop-By referring to Fig. 1 it will be observed that the two radio beacons or aerophares RBI and RBZ, which are preferably of a construction more fully described hereinafter, are lined up with the glide path for landing airplanes on a runway. This is not a necessary requirement in that the runway could be located a considerable distance away and need not be in a line with these beacons, but it is, however, preferably of a construction as illustrated. From a point above each of these radio beacons RBI and RBZ the ilying path of the storage loop consists of a left-hand semi-circular turn started from such beacon which path upon completion of this turn runs directly into the other radio beacon. In other words, these two radio beacons RBI and RB2 define a iiying path in a holding stack which has one-minute semi-circular turns the ends of which are joined by straight lines each 1.5 minute flying distance in length. These distances are expressed in minutes on the assumption that an airplane travels at, say M. P. H., and from these time values the actual distances can be readily calculated. Airplanes fly in this holding stack path in directions as indicated by the arrows.

If an airplane is called from this holding stack HSI for the purpose of consuming a variable amount of time in a holding loop such as HLI, depending on his location in the holding stack when he is called, he will if he is ying toward beacon RB?. immediately proceed to make a lefthand one-minute semi-circular turn. If the airplane is located directly over the radio beacon RBZ at the time he is called the time consumed in the stack, conveniently called the stack-loss time, will be one minute consumed during the semi-circular turn and 1.5 minutes consumed during the straight run making a stack-loss time of 2.5 minutes, which is the maximum stack-loss time under no-wind conditions. The holdingloop path is conveniently divided into five parts consisting of a straight run of out-time OT, a circling distance X, a one-minute semi-circular turn CT, another distance X, and an in-time IT. Since the out-time OT and the in-time IT are the same distance (expressed in time) each of a length to consume one minute (for minimum loop) the total time to be consumed in the minimum holding loop, illustrated by dotted lines in Fig. 1, may be readily determined by calculating the two distances X, which are equal, and by adding thereto the out-time of one minute, the in-time of one minute and the semi-circle time of one minute. This calculation of the distance X for minimum out-time, expressed in minutes, can readily be shown to amount to 0.098 minute so that 2X is a distance of 0.196 minute iiying distance. The distance X may be calculated as follows: The tangent of the angle X about the center of the circle is the radius divided by OT or 0.318/1 for the minimum out-time of 1, so that the angle is 1740 and expressed in radians is 0.3083. Multiplying this by the radius (0.318) we have .098 for X or 2X=0.196.

By referring to Fig. 1 it will readily be seen that if the stack-loss time is known the holdingloop time can be determined by subtracting the stack-loss time from the total time. It is also readily seen that if the semi-circle time CT of one minute is left out of the computer and since the out-time OT is equal to the in-time IT it would only be necessary to divide 2OT+2X by 2.

Since, however, the variable'part of 2X varies inversely with `the value of 20T it can readily be seen that if 20T is divided by a number slightly smaller than 2 the changing value of 2X may readily be compensated for. l

By again referring to Fig. 1 and the above calculation of X it is readily seen that for a maximum stack-loss time SLT of 2.5 `minutes the out-time OT and the in-time IT will each be one minute and under this condition the value of 2X will be 0.196 minute and the semi-circle time will be `one minute. Summing these values up it is readily seen that the total time to be consumed between the calling of an airplane from the holdingstack and the time of passing of this airplane over the b eacon RBI` when leaving the holding loop will be 5.696 minutes. It is also readily seen that for a minimum stack-loss time SLT (Zero) the value of 2X, conveniently called the unvariable part of 2X, will be `0.086 and then the out-time OT will be or 2.305. It should nowbe remembered that the purpose of the computer is to compute the heading angle and the out-time OT under various conditions.

Structure-Wa 3.-Referring for a moment to Fig.3 of the drawings, in this drawing has been illustrated a theoretical computing machine which has been illustrated primarily for the purpose of getting a better understanding of the elementary computations that the computer is called upon to make under no wind conditions. In this schematic showing of Fig. 3 a shaft I5, which is connected to one terminal of a suitable source of current, has associated therewith a contactarm I6 which is weighted to its normal position against stop I9 by a weight I1, fastened to this'arm I6 by a set screw I8. This arm I6 is provided with a pointer to point out the stack-loss time and the proper heading angle at which the airplane is to fly into the holding loop I-ILI This arm is held in its normal position against the stop I9 by gravity acting upon weight I 'I. This weight I 'I is heavy enough to return the apparatus to its normal position in spite of the fact that both of the motors MI andM2, each of which may include gear reduction, the shaft 2I and the pinion 22 and gear 23 must also be returned to their normal position.

It is readily seen that if 'the quantity 2X heretofore mentioned Vwere not `a factor and if the semi-circle time CT of one minute were omitted from the machine, leaving 4.5 minutes in the computer, it would only be necessary for the motor M2 to divide by two, that is, to have a speed double that of the speed of motor MI to cause the lamp 25 (Fig. 3) to be lighted when the stackloss time SLT and the out-time OT have both been consumed. Let us assume for the moment that the portion 2X is disregarded and that the y motor M2 has a speed twice that of a speed of the motor MI. Let us also assume that the operator calls an airplane from the stack I-ISI of Fig. 1 when it flies directly over the beacon RB2 and that the-operator at this time closes the switch 26. The motor MI will now be operated and cause operation of the shaft 2| at a speed of 1 R. P. M. From this it will be seen that when the airplane reports `passing over beacon RBI a time of 2.5 minutes will have been consumed and the contact arm I6 will have moved a distance-signifying 2.5 minutes. As the pilot reports passing over the beacon RBI the operatorl 6 will depress the pushbutton 21 to thereby deenergize the motor MI and energize the motor M2 and under the assumption above made this motor M2 will operate at double speed so that it will grind out, so to speak, the out-time OT and the in-time IT simultaneously so that the arm I6 will engage the contact 28 and cause illumination of the lamp 25 at the expiration of the time OT. Under this condition the total time in the computer would be 4.5 minutes and the out-time OT would be 1 minute.

This computer illustrated in Fig. 3, however, has a total time of 4.4157 minutes for reasons hereinafter pointed out. It is thus seen that under the assumptions just made the motor MI will grind out, so to speak, the stack-loss time and the motor M2 will operate at twice that speed and will simultaneously grind out both the outtime OT and the in-time IT. Let us now determine what the speed of the motor M2 should be instead of the speed `2 R. P. M. above assumed, to as nearly as possible give consideration to variations in the value of 2X.

As above pointed out for maximum stack-loss time of 2.5 minutes the value of ,each of OT and IT is one. The value 0i' 2X is 0.196 and the circle time is l so that the total time is 5.696. Also, if the stack-loss time is a minimum, namely, O, then 2X equals 0.086 and OT' equals Ii we now take the circle time CT from this total time the total time of the maneuver will be 4.696 but thisis not the total time built into the flight predictoncomputer or calculator, for the simple reason that the variable part of 2X varies substantially inversely with the value of OT, that is, as OT increases the variable part of 2X decreases, and consideration must be given to the variable portion of 2X. Since we want to use a lower speed ratio than 2 R. P. M. to compensate for variation in 2X we must reduce the total time by a constant which we will call K. If we now consider g to be the speed ratio of the speed of motor M2 to that of the motor MI we may write out the :following equation:

4.5-K-SLT g where 4.5 is the total time in the computer when 2X is disregarded, SLT is the stack-loss time, K is a constant brought into the computer in order to give consideration to the value of 2X, and g is the desired speed ratio or gear ratio, as the case may be, to give consideration to this value 2X. In order to determine the apigiroxin mate values of K and y we may assume the two extreme limits; nrst maximum stack-loss time SLT and one minute out-time OT and then the other limit of Zero stack-Joss time SLT and magie mum out-time OT-of 2.305. Substituting these values in the equation above we have for the rst set of values mentioned and we have for the second set of values where the stackloss time is Zero. Solving these equations for g we have 7 and from'the second situation it 'also equals fat-'K vSolving for K lwe rst get the expression multiplying through by 2.305 We get 4.61-25305K=4.5-K or 1.305K=0.11 r K=0.0843

Note that 0.11 is the variable portion of 2X and that 1.305 is the variable portion of OT. Therefore K is the variable portion of X divided by the variable portion of OT.

Substituting the value of K in either of the above equations we have g- .1.9157. Substituting now the values of both K and g in equation OT=4.5-K-SLT 'We have 4.4157-SLT 0T 1.9157

From the above considerations and from the structure shown in Fig. 3 we know that the total time in the computer is the stack-loss time SLT plus 1.9157 OT, so that if stack-loss time is 2.5 and OT is one We have a total time in the computer of 4.4157. Also, when stack-loss time is 0 we know that OT is 2.305 so that the time in the computer is 1.9157 2305 which also gives us 4.4157. It is therefore readily seen that the total time in the computer is the total actual time of 5.5 minutes minus the one-minute semi-circle time, which was purposely kept out of the computer, minus the value K of 0.0843 leaving a balance of 4.4157 minutes. If we now assume that the speed of the motor M2 shown in Fig. 2 is such as to rotate the shaft 2| at 1.9157 R. P. M. and if the sweep of the contact I6 when driven by the motor MI requires 4.4157 minutes to light the lamp 25 then the apparatus conventionally illustrated in Fig. 2 will light the lamp 25 substantially when the time OT has been consumed, assuming that the operator closed the switch 26 when the airplane was called from the holding stack HS-I and assuming that he depressed the push button 2 when the pilot reported leaving the holding stack HSI and entering the holding loop HLI.

Attention is directed to the fact that the total time in the computer is less than the total time between the landing of the airplane and its be-i ing called from the holding stack to an extent of minus one, minus the value of K and furthermore that this value K is equal to the variable portion of 2X, namely, 0.11 divided by the variable portion of O-T, namely, 15305. It should be understood that this gear ratio or speed ratio 1.9157 is not exactly correct for all situations and is in fact exactly correct only for the two values of OT used in calculating it. This is true because X varies as the angle under consideration Whereas out-time OT varies as the tangent divided by the sine of that angle and these two factors do not vary exactlyalike although the discrepancy is very small for small angles.

It will be seen that a scale of heading angles has been provided for the computer of Fig. 3. The particular heading angle to which the pointer points when the pilot reports exiting from the holding stack is theangle read by the voperator tothe 4puttana is th angle the putt must bear to the left of the beacon line RB2-RBI in making his holding loop. YIn practice this will be given in azimuth degrees by rsubtracting it from 360 for those situations where the holding loop is directly to the north of the landing strip or runway as shown in Fig. 1.

' Operation-Fig 3.-Let us now assume that an airplane is at the point 30 in the holding stack when the operator calls him to start a landing procedure and also that he closes the switch 25. The pilot will immediately make a left semi-circular turn and one minute later will be over beacon RBI. The contact arm I6 will have moved a one-minute portion of the total of 4.4157 minutes of the distance to the contact 28, namely, have moved a distance equivalent to 1 minute. The pilot now reports leaving the holding stack HSI andthe operator depresses the push button 27. The operator also reads the heading angle of 23.6 to the pilot as indicated to him by the pointer of arm I6. This stops motor MI and starts motor M2 and causes shaft 2l to rotate at the new and higher speed of 1.9157 R. P. M. After the motor M2 has operated for an OT time of 34157/19157, namely, 1.78 minutes the contact 28 closes and lights the lamp 25. The audible signal 3|, however, preferably sounds about 10 seconds earlier to give the pilot, as through the medium of the radio, a warning that he is soon to be ordered to make a procedural turn. subtracting twice the OT time of 1.78 from 5.696 and then subtracting 1 for stack-loss time and 1 for circle time, we have 0.136 minute to cover the 2X distance. From this it will be seen that even though the computer is not per cent accurate it gives subf stantially correct values and gives them very quickly. Although the computer shown in Fig. 3 was illustratedv to show a simple construction embodying some of the computing principles of the present inventionv it may be considered a modification of the preferred form of computer shown in Figs. 8A and 8B, if desired, and may be used at places where wind is a less significant factor.

Structure-Figs. 8A and 8B.In Figs. 8A and 8B, when laid above each other in staggered relationship, has been illustrated the preferred form of computer embodying the present invention. This computer in addition to the functions performed by the computer illustrated in Fig. 3 substantially accurately determines both the out-time and the heading angle irrespective of head or tail winds and irrespective of side Winds. This correction in the heading angle is the angle at which an airplane'must head to correct forin Figs. 8A and 8B and not found in the Fig. 2v

structure resides in the provision of automatic means for increasing the total time consumedbetween the calling of an airplane from the holdl ing stack and his arrival atthe point where he is in a landing position for all head winds, this ad ditional time being dependent upon such head wind and increasing' therewith and being automatically set up in the computer in accordance with vthe positio'assumed by the head wind and .ated position during this movement of the spider `85 from its out-time position to its normal position. In order to cause such hesitation of the spider 85 at an intermediate position, during its return to the normal position, a lock member |30 secured to the arm |3| secured to armature I I4 is provided. This arm |3| and this lock member |30 are held in a normal position against a stop |32 by a tension spring |33. If now the spider 05 assumes its abnormal out-time position energize.- tion of the electromagnet NMA will cause the lock I arm to move under the right-hand end of the spider 85 and will at the same time move the spider to an intermediate position in engagement -With this lock arm |30. The spider 85 will, however, have been operated slightly beyond its middle position and to a position where the toggle spring ||3 is in position to complete the stroke of this spider operation. The toggle spring 3, however, cannot complete this stroke because the lock arm |30 prevents such completion of the operating stroke. .I After a period of time, the magnet NMA being only momentarily energized, the slow acting feature of this electromagnet 'NMA will have dissipated the energy in its holding slug, or other retarding means, thereby allowing the spring |33 to withdraw the lock arm |30 from under the right-hand end of the spider 85 and thereby allow the toggle spring I I3 to complete the stroke of spider 85.

This spider 85 is provided With an insulated insert |35 which normally holds the contacts |36- |31 open. On the shaft 6| and secured thereto is a contact operator |40. As already pointed out the gear 15 and in turn the out-time shaft 6| are biased in a counter-clockwise direction through the medium of the spring |25. It is therefore apparent that a suitable stop should be provided to prevent too much counter-clockwise rotation of this shaft 6|. Such a stop engageable by contact operator is provided through the medium of the stop member |4| which is secured to the pinion |42 engaging the rack 65. From this construction it can readily be seen that the operated sliding position of the rack 65 Y determines the normal position of the shaft 6I. This contact. operator |40 in addition to comprising part of the stop means also serves to open the contacts I 44-I45 when the out-time shaft 6| has been operated to a predetermined extent` referred to hereinafter as the maximum stackloss or minimum out-time position. The shaft 6| is provided with a second contact operator |50 which is used for the purpose of iirst momentarily closing the contacts |5|-|52, thereafter opening and thereafter bringing the rotation of shaft 6| to a stop by engaging stop member |56. The exact position assumed by the out-time shaft 6| when such contact operation is performed is determined by the position in space that these contacts |5|-|53 assume. In this connection it should be observed that these contacts |5|-I53 as well as the stop member |56 are supported by the pinion |55. This pinion |55 is in engagement A with the teeth on the rack 66 so that endwise operation of the rack 66 determines the position assumed by the support which supports contacts |5|, |52 and |53 and stop member |56. It may also be pointed out that this pinion |55 supports and at times rotates the marker69 with respect to the dial 1| on which dial the unused stack-loss time is read through the medium of the indicating pointer 10. This marker 69 points out the location on the dial 1| where the pointer 10 will these contacts and closing the contacts |5|-I53 be-When the peep-peep warning signal is started and completed, that is, the width of the marker 69 signifies the duration of the sounding of the peep-peep signal. l

. f As already pointed out the racks 65 and 66 are operated in accordance with the position assumed by the head-wind and tail-Wind knob |60, the extent of this movement being dependent upon the shapes of the two cams and |65 which cause such movement. Also, rotation of this knob |60' cannot take place unless the knob |66 is pushed in against the tension of the spring |62. Such pushing of the knob 60 will cause the gear 98 to disengage from the particular cone gear with which it was in engagement and rotation of the knob |60 thereafter will cause corresponding rotation of the toothed pinion |63, the teeth of which are in engagement with the peripheral teeth on the hub |64 of the gear 91. In other Words, pushing in of the knob |60 and rotation of this knob, after which the knob will be returned by the spring |62, will cause the gear 93 to engage another gear of the cone |60. The particular gear selected depends upon the direction and extent of rotation of this knob |60. It may be pointed out at this time that the synchronous motor MA, one for each unit of the calculator, is normally disconnected from the source of alternating current whereas the motor MM is preferably continuously connected to a source of alternating current, with the exception, of course, when the computer is not in use.

Heading angle seZectio11..--As already pointed out the pointer 12 as Well as the associated dial 13 are both operated to determine the heading angle at which the pilot is to head into the holding loop. The pointer 12 is directly connected through the medium of shaft 62 to the slotted crank |10. This slotted crank normally assumes a Vertical position, that is, assumes a vertical position when the drift-angle knob |69 assumes a Zero position. As already pointed out this drift knob |69 through the medium of pinion |68 controls the endwise movement of the rack 64. It is now desired to point out that this endwise position assumed by the rack 64 determines the initial angular position assumed by the slotted crank |10. This is accomplished through the medium of frame |1|-|14 which consists of a frame including radius arms I1| and |12 and rivet |14. This frame |1|-|14 is very rigid and the rivet or pin |14 is moved about the pivot |61 and up and down in the slot of crank arm |10 dependent upon the position it assumes in the slot |16 of plate |15 and the position assumed by this plate |15. The radius arm |12 is preferably so long that the pin |14 moving about pivot |61 moves substantially vertically in the slot of arm |10. The raised position of this plate |15 is determined by the position assumed by the crank pin |18 in the arcuate slot |11 which is dependent on the position assumed by pointer 10. This plate |15 is mounted for up and down sliding movement in channels |8| and |62 all as more fully pointed out hereinafter. The shapes of the arcuate slots |16 and |11 will be more fully discussed hereinafter attention being directed to Fig. 11 of the drawings which shows an accurate front view of one particular form this plate |15 may take.

In order that the dial 13 may be operated accumulatively from two dierent apparatuses an epicyclic gear train is provided. This epicyclic gear train includes an annular gear AG secured, as by pins |84, to flange |85, which is in turn `13 secured to the dial 13, as through the medium of a hub |36, and includes two planetary gears PG! and PG2 and the sun gear SG. vThe sun gear SG is secured toa flange |87, as through the medium of a hu'b |88. The flange |81 is provided with a crank arm |89 which supports the crank pin |18 heretofore mentioned. The planetary pinions PGI and PGZ are pivoted on pins Id! and |92 which are in turn supported in the planetary pinion supporting gear E89. This planetary pinion supporting gear I9() is rotated in accordance with the position assumed by the orientation knob |95 as through the medium of gear l 96 and idlers |91 and |98. It is thus seen that the dial 'i3 of the heading angle indicator may be rotated by both the orientation knob |95 and b y the crank |89. This crank |39 is` biased against the driving member 20| through the medium of the spiral spring 200 and this driving member, during motor operation of the gear l5, is driven in a counterclockwise direction so that the crank |89 will by action of spring 2t@ follow the movement of the driving member 2l! I. In this connection it should be noted that this driving member 20| is supported `by the gear 205 and that this gear 205 is driven by gear l5 through the medium of idler gears 2il2, 293 and 204. The spiral spring Elli! is an-chored between the flange Il` and the anchor plate 208 which anchor plate Zll is adjustably anchored to the gear 205 as through the medium o-f a-lock pin 209.

The flange |81 is preferably provided with very closely spaced narrow and sharp teeth for the purpose of allowing this flange to be locked, as through the medium of the toothed lock member 2M), in many different positions. This toothed lock member 2|() is preferably pi'voted, as indicated, about the pin 2li and is normally urged out of locking engagement Awith this toothed `flange |81 as through the medium of theA spring so long as the toothed ilange |81 is 'not locked,

namely, in accordance with stack-loss time, and that the pointer 12 is operated initially in accordance with the extent of rotation of the `drift knob |69 and is supplementally operated to an extent dependent upon the extent of movement of the pin |13 toward the left in the slot Il? which is also dependent upon the extent of `rotation of the shaft EI in measuring stack-loss time. The eX- tent of downward inovementlof the plate |15 is dependent upon the extent of rotation of the shaft 5| prior to the time the toothed flange |81 was locked (stack-loss time) in thatthis flange |81 remains stationary so long as it is locked. Continued rotation of gear 2115 is, however, permitted by the yielding action of spiral spring Zilli. Since downward movement of plate |15 `causes downward movement of pin |14 in the slot of crank |18 this crank ITB and the shaft t2 on which it is mounted will be turned if this crank already assumed a slanting position. In fact the slots |76 and Ill in plate |15 are-of suchshape that the extent of this supplemental rotation of crank'l'l is a product of the extent vof its initial rotation of shaft 62 from normal by knob |59 (stack-loss time). l l' operation of the computer of Figs. 8A wat` `:ne (no wind)`.etu`s vassume that the apparatus `illustrated in Figs. 8A and 8B is in its normal condition, as illustrated, and that the operator calls an airplane from *the stack HSI (Fig. l) as he is liying -southwardly over the radio beacon RB2. The partcula-1` normal condition illustrated, there lbeing three normal conditions, is one Where the unit 'C' (see Figs. '7, 8A and 8B) of the computer has been operated to a minimum holding loop position" (maximum stack-loss position). That is, a ho-idling loop having an out-time OT of lone minute. `Obviously Vother stack sizes and time values maybe used. At such minimum loop posi- `tion for any unit the contacts IM-Ill are open (contacts IBB-137 having not yet closed) and 'in so *doing remove energy from the timing motor M (Fig. 4) and from the motor MA (Fig. 8B). The circuits shown `in Figs. 6A, 6B and 6C and the dials shown in Fig. 126 -s'how the unit `A in its minimum out-time position. This `calling of the airplane from -the holding stack occurs when the green light G of unit A-on each of the panels X, J and Z (Figs. Aand 7) of the `calculator become lighted unless the lcomputer already stood in minimum holding loop pos-itiion as is now the case as illustrated by the circuits in Figs. 6A, 6B and 6C. Let us consider the operation, however, with the unit A of the computer in its zero operated position. Simultaneoi-isly with such lighting of this green lain-p the motor MA (Figs. `6A and 8B) is started operating to cause the pinion 9|) to operate at the speed of l R. P. M. This simultaneous action is due to picking up of relay AGR (Fig. 6A) which controls the lam-p G, board X, unit A, through its front contact 52 and motor MA through its iront contact 53. The operator, in a suitable tower near the airfield on the ground, also inserts a 'token identifying that airplane in token jack OTJ for unit A, panel X (Fig. 7), altitude 1200, also designated 3 Il (Fig. '7) resulting in the closure of contact 3|@ (Fig. 6A) which results in the picking up of lock relay XL, unit A (Fig. 6A), and in the llashing of green light G, unit A, panel X, and in the lighting of the purple light P for the units A .of all three panels X, J and Z (Figs. 6A, 6B, 6C and '7). The operator then depresses push button unit A, panel X (Figs. 6A and 7) which results in the picking up of relay YF, panel A (Fig. 6A), through front contact M5 of relay GRP, which causes the green light G, unit A, panel X to be changed from flashing to steady. This second steady indication obtained through front contact 4D3 of relay YF is, however, distinctive from the nrst steady indication in that the associated purple light is also lighted. The relay` GR, panel A, remains stuck up through a stick circuit including a normally closed contact of push button 2 and wire's254 and 286, unit A, panel X, .its former stick circuit through back Contact 3 I El of its associated relay YF having been broken. The unit A of the computer illustrated in Figs. 8A and 8B now operates to measure the maximum stackdoss time, namely, the time consumed by the airplane flying in the holding stack from beacon RBZ toward beacon RBI (Fig. 1) of 2.5 minutes.

With the computer of 8A and in its zero condition the pointer l5 is positioned on the dial 1| to indicate 2.5 minutes which corresponds to the maximum stack-loss time. lSince the airplane under consideration was assumed to be over the beacon RBB, when the computer started operating and when the airplane was called from the holding stack, this airplane will consume this `maxinmm stack-Joss time of 2.5

15 minutes by the time it iiies over the beacon RBI and leaves the holding stack and the pointer 10 of unitA will indicate zero as itdoes in Fig. 16.

The gears 16 and 18 (Fig. 8B) are of the same diameter and for the particular construction assumed the gear 15 is of a diameter ten times that of the diameter of pinion 90. With such gear ratios, other gear ratios may obviously be used, the rotation of 2.5 revolutions of pinion 90 (2.5 minutes) will cause gear 15 to rotate 1A revolution to thereby cause the pointer 10 to indicate zero on the dial 1| at the end of the time consumed by the airplane in the holding stack HSI (Fig. 1) under the condition assumed.y As the pilot of the airplane under consideration reports flying over the beacon RBI in the northward direction, that is, as he leaves the holding stack, he reports this event to the operator who reads the heading angle indicated by pointer 12 on dial 13 and then depresses push button 2, unit A, panel X (Figs. 6A and 7) to thereby cause deenergization of the relay GR, unit A, by the opening of the stick circuit for this relay. This causes deenergization of slow dropping repeater relay GRP and also causes the yellow lamp Y, unit A, panel X to flash through va circuit including back contact 320 of this relay GR. It also causes a prolonged momentary energization of the electromagnet OMA (Figs. 6A and 8A) through a circuit including front contact 62| of relay GRP and back contact 385 of relay GR.

Depression of push button 3, unit A, panel X, by the operator in response to the pilot's repeat-back of the heading angle, picks up relay YS which by the lifting of its contact 320 changes the lamp Y, panel X, unit A, `from a Ilashing to a steady light. Relay YS, unit A, is now stuck up through a `circuit including back contact 32 of relay RS and its stick contact 323.

This momentary energization of the magnet OMA mentioned above during its initial loperation causes the rod IIB (Fig. 8B) to be pulled down to thereby allow the spring |2| to apply the brake |20 away from its stop |22 and against the gear 15, to prevent retrograde operation of this gear due to the tension of the spring "|25, this brake |20 being a ratchet brake to prevent only counter-clockwise rotation of gear 15. Continued movement of the armature II5 of the magnet OMA causes the spider 85 to be operated to its out-time position to cause engagement of gear 15 with pinion 9| instead of pinion 90, where it is held by toggle spring ||3. Gear shifting having now taken place the gear 15 is now driven at the higher speed through the mediurn of the out-time pinion, or dividing pinion 9 I. Dial 13 is however no longer rotated because flange |81 is now held by brake 2I0; rotation of gear 205 is however permitted by the yielding action of spring 200. This pinion 9|, under nowind condition, operates preferably at a speed of 1.9157 R. P. M. in the particular construction shown. This is true because the shaft 68 operates at this same speed and the bevel gears I G and |01 have a gear ratio of one to one.

For reasons already pointed out in connection with the simplified computer of Fig. 3 the total time between the 2.5 position on dial 1I and the time that contacts II-I53 are closed is, under no-wind conditions, 4.4157 minutes. subtracting the stack-loss time of 2.5 minutes from the total time of 4.4157 minutes set up in the computer leaves a difference of time in thel computer of 1.9157 minutes. Since the speed of the pinion 9| is 1.9157 R. P. M. it will require just one minute of actual time to cause the contacts |5I--I53 to close after the pilot has left the holding stack HSI. Or in other words, the out-time OT will be one minute as it should be from considerations given to the flying pattern illustrated in Fig. 1 hereinbefore. This out-time of one minute is, however, not yet of any importance because the pilot is just leaving the holding stack HSI, and it is necessary for the operator, as above pointed out to instruct the pilot at what azimuth he is to ny into the holding loop HLI (Fig. 1).

As already pointed out, in the particular embodiment of the invention illustrated, the pitch diameter of gears 16 and 18 are the same and the pitch diameter of pinion 90 to gear 15 is in the ratio of one to ten, the pinion 9| being of the same diameter as pinion 90. Also, in this particular embodiment of the invention illustrated, the gears 15 and 205 preferably have the same pitch diameter and the pitch diameter ratio of gear 202 to gear 203 is as 2.217 is to 1. This gear ratio is chosen so as to cause rotation of dial 13 an extent equivalent to 20.3D (35.3-15, see Fig. 13) during 2.5 minutes of rotation of shaft 6| (maximum stack-loss time) in order to indicate the proper heading angle. Also, the epicyclic gear train used for driving the dial 13 is of a construction such that the pitch diameter of planetary gears PGI and PG2 are each half the pitch diameter of the sun gear SG, and the internal pitch diameter of the annular gear AG is twice that of the pitch diameter of sun gear SG. In other words, if the planetary pinion supporting gear |90 is held stationary and sun gear SG is rotated then the annular gear AG will rotate in the opposite direction half as fast as does the sun gear SG.

Coming back now to the operation of the computer, it will be remembered that during the time the pilot flew in the holding stack, which was 2.5 minutes, the gear 15 was rotated clockwise by the pinion 90 through 1A of a revolution, that is, through an angle of 90. This 90 rotation of gear 15 will cause the gear 205 to rotate counter-clockwise less degrees to the extent of the ratio of the diameters of gears 203 to 202, namely, to an extent of 90 divided by 2.217 or through an angle of 40.6. Since the dial 13 rotates half as fast as does the gear 205 this dial 13 rotates in a, clockwise direction to an extent of 20.3 so that the pointer 12 instead of indicating the original 345 now indicates 324.7". This is the heading angle that the operator will instruct the pilot of the airplane to fly at as he leaves the holding stack HSI (Fig. 1). This angle denes degrees azimuth and is equivalent to ying to the left of due north to an extent of 35.3. This angle is the same as the one indicated by the apparatus illustrated in Fig. 3 and is the largest no-wind heading angle.

The pilot will now fly in the direction azimuth 324.7 which is along the line OTI in Fig. 1 of the drawings. It will be remembered that at the time this angle was read to the pilot the spider was operated from its normal to its out-time position and that the gear 15 is now rotated at a speed of 1.9157 times that of its original speed and that after one minute of operation at this increased speed the shaft 6| will have rotated to an extent to close contacts |5||53. In this connection it will be pointed out that the contacts ISI-|52 were closed for a period of approximately ten seconds prior to the closing of assenze the contacts |5||'53. This prior closing'v of the contacts |5| |52 closes a circuit including these contacts ISI-|52 (Fig. 6A), front contact 325 of relay YS and winding of relay RS, unit A (Fig. 6A). The picking up of relay RS sounds a so'called peep-peep signal, both directly to the operator and indirectly through the medium ofv the radio communication apparatus to the pilot on the airplane. The operators headsets of this radio communication apparatus have been illus- I;

trated at 335 in Fig. 7 of the drawings, the microphone receptacles being shown at 334. If desired each operators set may employ a diiierent carrier frequency so that simultaneous conversations may be carried on by a plurality of operators. This sounding of the peep-peep signal 32% (Fig. 6A) is accompanied by the lighting of the red lamp R, unit A, panel X (Fig. 6A).

Picking up of relay RS, unit A (Fig. 6A), by the opening of its back. contact 322 drops the associated relays YF and YS. Dropping of relay YS opens the pick-up circuit for relay RS at its front contact 325. About l seconds later contacts ||`|52 open and contacts |5|-|53 close causing the steady red light to change to a flashing red light. Also since this iiashing is comparatively slow, say at one second intervals, the

relay RS, unit A, will drop at least momentarily and open its stick circuit at its stick contact 328 so that it will remain down. The red lamp R,

unit A (Fig. 6A), will keep on flashing due to the flashing energy supplied by contacts |5||53. Also, contacts 52--5I--53 are break-before-make and this also assures the dropping of relay RS. Further turning of the shaft 0| will, however, be prevented by reason of contact operator |50 engaging stop |50. No harm will be done in that motor MM will not be stalled by reason of slippage allowed by slip clutch IUE-|05.

` The operator will now momentarily depress push button 4, unit A, panel X, which will, through the medium of wire 210, result in the momentary energization of the normal magnet NMA (Figs. 6A and 8B). Lock relay XL (Fig. 6A) will not drop because the token still holds token contacts 3I' (Figs. 6A and 9) closed. This Aener,g',fization of the magnet NMA will cause its armature ||4 (Fig. 8B) to be attracted and as it starts moving the spider 85 in a clockwise direction a completion of the movement of the stroke of this spider 85 is prevented by the lock member |302 coming underneath the right-hand end of the spider 85. The spider 85 will, however, have been operated beyond its center position where gear 16 is disengaged from both of the pinions 90 and 9|, and the toggle spring |13 will tend to complete the stroke of the spider 85.

As conventionally illustrated the normal magnet NMA is slow dropping and since it is only momentarily energized its armature will be released only after its drop-away period has ex pired. Such releasing of the armature ||4 will, after the spring |25 has returned shaft 6| and pointer to its original position, cause the lock member |30 to disengage from .beneath the righthand end of the spider 85 to thereby allow the toggle spring ||3 to complete the stroke of the spider 85 toward its normal position. This 4hesitation of the spider 85 in an intermediate position allows the spring |25 to return the gear 15 together with all of the .gears and .pinions con nected thereto so that the apparatus again assumes its zero position as illustrated in Figs. A8A and v.8B of the drawings.

When the pilot reports clearing altitude 1200,

"in a direction toward the ground, the operator will remove his token, identifying that airplane, from token -jack OTJ at 3|1 and will insert it in ground defining token jack OTJ at 330. When the airplane has landed the pilot so reports and the operator removes the token from token jack 330. This removes pick-up energy from lock relay XL, unit A (Fig. 6A).

A second .momentary depressing of push -bu'tton 4, unit A, panel X, now opens momentarily the normally closed Contact '336 of this push but# ton 4 included in the stick circuit for lock relay XL, uni-t A, including wire 20| and stick ccntac't 329 -of the relay XL. Since removal of the' token has opened the pick-up circuit for this relay XL this relay will now drop. Dropping of 'this relay XL ex-tingushes the purple lamp P on the unit A panels for each of panels X, J and Z (Figs. 6A, 6B, 6C and 7). All of the lamps and all 4of the computer apparatus have now been re-` stored to their normal conditions except that possibly now unit B of the computer has been oper.- ated to the minimum loop position where contacts |44|45 of this unit open and stop all of the motors M, MA, MB and MC. For reasons pointed out lhereinafter a monitor must also move Vhis token on his board (see Fig. 9) to properly contr-ol the lights on the token `board X (Fig. 7). Operation-Figs. 8A and 8B (left wind) .-Since the effect of the west wind will be such that when an airplane is iiying northwardly it will have to point its ncse to the left of north in order .to compensate for suoli wind the drift angle due to a west wind will be called a minus drift angle and if we assume that this west wind is such as to result in a drift angle of 10 the operator will turn his drift-angle knob |69 to the posi tion -i0. Such movement of knob |00 (Fig. 8B) will cause counterclockwise rotation of pinion |53 and will cause the rack |54 to be moved to the left to an extent that the slotted .crank |10 and pointer 12 assume substantially a position 14.7 to the left of normal. This willin turn cause the pointer 12 A'to indicate 3303* azimuth instead of the normal 345 azimuth position (Fig. 7). This is the proper position for pointer 12 under the assumed wind condition and zero stack-loss time. v

Let .us now assume that the operator calls an airplane from the holding stack HSI (Fig. i9 in response 4to the lighting of the green lamp G, unit A, panel X (Figs. 6A and 7), just as the airplane is iyi-ng over the radio beacon HB2. By reason of the vfact that this west wind will have very little effect on the speed of the .airplane while in the holding stack the airplanewitl arrive over the .beacon `Rl-Zti substantially '2.5 minutes after 'the computer unit A of Figs. 8A and 8B was initiated'. During this 2.5 minutes Aof operation lof the .gear 15, through the medium `of .the pinion 90, this .gear 75 (Fig. 8B) will have vrotated through `an angle of substantiallyf 1n-a clockwise direction, and in turn will have caused counterolockwise rotation .of -the .gear 205 to ran extent of 40.6. As a result .of this operation Ithe crank pin |18 moves counter-clockwise inthe slot :|11 -of the multiplyingplate |15 to an extent 10i 40.6".V This movement vof the crank lpin |18` in slot |11 will :cause downward movement of the multiplying plate I 15 as is apparent from the shape' rni-this slot |11 (see Fig. 11). This multiplying vplate also movedy downwardly to the same extent vduring the particular operation ef this apparatus heretofore considered Ibut in that ycase the slotted crank |10 was in a vertical posi- 

